Known cordless power tools came in a variety of assemble and play modules. In U.S. Pat. No. 4,374,354 the tool module, for example a toothbrush, fits into one end of a power module that contains both a d.c. motor and a battery. The other end of the power module fits into a battery recharge module that receives power from an a.c. power main. Although this unit contains electrical isolation of the motor and battery, the isolation can fail during recharge, resulting in damage to the motor.
Other cordless power tools solve the isolation failure problem by placing the motor and battery in separate modules. In U.S. Pat. Nos. 3,533,119 and 5,170,525 the battery module has both an a.c. plug unit and a d.c. plug unit. The a.c. plug unit is operable for recharge to plug directly into an a.c. main and the d.c. plug unit is unused and therefore an open circuit. The motor module also contains a mating d.c. plug unit which is active to receive battery current when plugged to the battery module d.c. plug unit. The motor module also includes an a.c. plug receptacle mounted in dielectric material so as to be electrically inactive when plugged with the a.c. plug unit of the battery module. That is, the a.c. plug units perform a purely mechanical coupling function during plug and play.
Although the cordless power tools disclosed in the aforementioned patents avoid the isolation problem during recharge, each requires numerous parts resulting in high cost.
An object of this invention is to provide a novel and improved cordless modular power tool.
Another object of this invention is to provide a cordless modular power tool that uses the same plug unit terminals for supplying d.c. current to the motor and for receiving a.c. current from an a.c. outlet for battery charging purposes.